This invention relates to temperature compensated rotary fluid meters. While this invention may be applicable to rotary meters which measure the flow of many types of fluids, it will be explained, by way of example, with respect to meters which measure the flow of gas for which it is particularly advantageous.
The density of a fluid, such as natural gas, used for producing heat, and thus its heating capability per unit of volume delivered, varies inversely and proportionately with changes in the temperature of the gas according to the principles of Charles Law. That is, the density of gas, and its heating capacity, decreases with increases in temperature and increases with decreases in temperature. The cost of gas delivered to a customer is normally billed at a set amount per unit of volume, at a selected density, which is measured at a preselected base temperature such as 60xc2x0 F. Where transmission pipeline pressure is constant, variations in gas density due to temperature changes result in an under-registration of gas heating capacity flow through the meter at temperatures below the base temperature and an over-registration of gas heating capacity flow through the meter at temperatures higher than the base temperature. Many large gas users require suppliers to use a temperature compensated meter to correct the readings of gas meters due to variations of the temperature of the metered gas.
There are many types of rotary fluid meters which have been developed. Each of these meters includes one or more impellers which rotate at speeds that vary with the volume of fluid flowing through the meter. The rotation of an impeller is used to turn one or more mechanical indices in a register used to show the volume of a fluid, such as gas, which passes through the meter. Temperature compensated fluid meters normally include a temperature transducer which converts changes of temperature into some type of motion and a register with either just a temperature compensated index or with a temperature compensated index and an uncompensated index. Temperature compensated meters also include a transmission assembly for directing uncompensated revolutions from the impeller to the uncompensated register (if one is used) and for varying the uncompensated revolutions in proportion to the changes in temperature of the fluid being measured from a selected base temperature, as well as a mechanism for interconnecting the temperature transducer with the transmission assembly. Previous temperature compensated fluid meters also include register covers which not only fit over and protect the index or indices, the transmission assembly and associated mechanisms, but also allow for the attachment of various meter accessories, such as automated meter reading devices, pressure compensating devices and the like, to the covers.
Many of these temperature compensated rotary meters have certain disadvantages which have affected their performance. For example, certain of these meters utilize temperature transducers with bimetal elements or transducers with helical structures which produce a rotary motion with a low driving force in response to changes in temperature. The interface of these transducers with adjustment mechanisms in the meters typically results in a non-linear motion, producing undesired errors in the temperature compensated measurement of gas. Other temperature compensating meters use intermittently operating devices in their transmission assemblies to provide a temperature compensated measurement of gas. It is necessary to prove all meters to determine their accuracy. The use of intermittently operating devices for temperature compensation requires a more difficult and relatively uneconomical, larger-volume throughput of a fluid being measured, such as gas, to prove these meters to compensate for the time intervals between the periods during which these intermittently operating mechanisms are idle.
Some temperature compensated fluid meters use the combination of a cone, a cylinder and a transfer ring surrounding the cylinder in a transmission assembly for varying the uncompensated revolutions from an impeller in proportion to changes in temperature of the fluid being measured. However, these meters feature a non-linear interface with their transducers. Additionally, the cone, cylinder and transfer ring are typically machined from hardened metal. The axis of rotation of the cone is set at an angle with respect to the axis of rotation of the cylinder so that the surfaces of the cone and the cylinder are parallel with one another. The transfer ring is mounted so that it contacts the surfaces of both the cylinder and the cone and is in a driving relationship between them so that a traction force results. The transfer ring is also transferred along the length of the axis of the cylinder in response to changes in the temperature of the fluid being measured to change the relative speeds of rotation of the cylinder and the cone. The use of this type of mechanism for temperature compensation in fluid meters has been limited because the precise fit needed between the cone, the cylinder and the transfer ring to prevent the mechanism from binding up or otherwise malfunctioning has required relatively expensive precision machining of these components to precise dimensions with tight tolerances and additional adjustment mechanisms for traction adjustment Temperature compensated fluid meters often have plastic register covers to protect the register and its one or two indices, its transmission assembly and other components extending from the register end of the meter. There is often a requirement to mount one or more accessories, such as automated meter reading devices or devices for generating pulses, on a register cover. The weight of these accessories has required that some register covers have separate structures to support them. Support structures have included a number of longitudinally extending rods attached to the meter at one end of a register cover and extending to contact the distal end of the cover to support accessories on the cover. Such support structures add to the cost of a meter and make it more cumbersome to assemble and maintain.
A temperature compensated rotary fluid meter for measuring the volume of a fluid flowing through it includes a meter housing which has a pressurized chamber in which fluid flows. A meter impeller assembly extends into the pressurized chamber so that one or more impellers rotate in response to the flow of fluid through the meter.
A temperature transducer has temperature sensing components, including a sensing bulb and a bellows, mounted substantially fully within the fluid flow chamber. The sensing bulb contains a liquid which expands and contracts with temperature changes and includes a bellows having an outside surface in contact with the liquid to react to liquid forces exerted due to expansion or contraction and having a moveable end in contact with the liquid and a stationary end. An actuator rod is attached to the moveable end of the bellows and moves substantially linearly and substantially continuously and proportional to theoretical temperature adjustment in a first direction as the bellows contracts when the liquid expands with an increase in the temperature of the fluid and moves respectively in a second direction as the bellows extends when the liquid contracts with a decrease in the temperature of the fluid.
The fluid meter also includes a transmission assembly and a register assembly which has at least a temperature compensated index for recording a volume of fluid flowing through the meter which is compensated for changes in the temperature of the fluid. The transmission assembly also includes a number of components which cause the temperature compensated index to adjust its measurement substantially linearly and substantially continuously for a particular volume of fluid in response to temperature changes.
These components include a cylinder having a cylindrical surface and a cylinder shaft which is radially stationary with the cylinder, while rotating in a mounting assembly at both of its ends The transmission assembly further includes a cone which has a conical surface and a cone shaft, radially stationary with the cone while rotating in a mounting assembly at both of its ends. The cylinder shaft and the cone shaft are in the same plane with one another and are located at an angle with respect to one another so that adjacent portions of the cylindrical surface and the conical surface are parallel to each other. A spring is in contact with said cone and has a spring force to bias the cone toward the cylinder. The cylinder shaft is operatively coupled to the impeller to cause the cylinder to rotate as the impeller rotates, while the cone shaft is connected to the temperature compensated register.
The transmission assembly also includes transfer ring which has a ring height and encircles the cylinder in driving contact with the cylindrical surface and the conical surface due at least in part to the spring force on the cone to cause the cone to rotate in response to the rotation of the cylinder. A transfer mechanism is interconnected with the transfer ring to move the transfer ring in a direction parallel to the axis of rotation of the cylinder. The actuator rod is interconnected with the transfer mechanism to cause the transfer mechanism to change the position of the transfer ring along the axis of the cylinder in response to changes in the temperature of the fluid being measured, thereby changing the speed of rotation of the cone with respect to the cylinder for a particular volume of fluid as the temperature of the fluid changes.
In one embodiment of this invention, the mounting assembly for the cylinder shaft includes a pair of elastomeric expanders within it, each of which extends circumferentially as a component of the mounting assembly. Additionally, the cone is slidably mounted on the cone shaft, and a spring is in contact with the cone to bias the cone on the cone shaft towards the cylinder.
The cone and the cylinder are mounted at positions such that said conical surface and said cylindrical surface are at a preselected distance from one another which is less than the transfer ring height during the rotation of the cone when the cone reaches the limit of its travel on the cone shaft. Thus, a traction force is exerted on the portion of the transfer ring that is between the conical surface and the cylindrical surface. The traction force cause the elastomeric expanders in the mounting assembly for the cylinder shaft to flex, in response to this force, by a predetermined amount that results in minimizing the effects of discontinuities in the size and shape of the ring, the cylinder and/or the cone during their rotation.
In accordance with another aspect of this invention, the fluid meter includes a register cover comprising an elongated housing, made of plastic material, that has a rounded cross section, a length, a meter end connectable to the meter and a closed end in which an opening may be made if accessories are to be connected. The register cover includes a mounting flange on its meter end, while its closed end is constructed out of plastic material. The mounting flange has a plurality of mounting holes in it for receiving mounting bolts used to connect the register cover to the meter housing. The register cover further includes at least one side rib, which is molded onto the outside of the housing and extends from a location adjacent each of the plurality of mounting holes substantially along the length of the housing. In one embodiment of this invention the at least one side rib comprises a pair of ribs, one mounted on each side of each mounting hole. A radially extending closure rib, corresponding to each of the at least one side ribs, is located within the register cover, on the closed end and begins near the end of each of the at least one side ribs to which it corresponds and extends toward the center of the closed end. In one embodiment of this invention, the closure ribs terminate at a circular flange on the closure.
This invention does not reside in any one of the features of the temperature compensated rotary meter disclosed above and in the Description of the Preferred Embodiments and claimed below. Rather this invention is distinguished from the prior art by its particular combination of features of a temperature compensated rotary meter. Important features of this invention have been disclosed in the Detailed Description of the Preferred Embodiments of this invention. These are shown and described below to illustrate the best mode contemplated to date of carrying out this invention.